Sensorless control in a permanent magnet machine

ABSTRACT

An apparatus and method for providing improved sensorless control of permanent magnet motors is described. Induced electricity from at least one winding set is used to determine rotor position and provide feedback to a commutation circuit driving at least another winding set isolated from the first.

BACKGROUND OF THE INVENTION

To effectively drive a permanent magnet synchronous motor (PMSM), themotor control system requires accurate information on rotor position.Sensors such as Hall sensors may be used to sense rotor position,however this increases cost and weight, decreases reliability, andsubjects the motor to temperature limitations imposed by the operationallimitations of the sensors.

Sensorless control is known, and typically involves estimation of therotor speed and/or position based on induced EMF or back-EMF occurringin an unenergized main or auxiliary stator winding. One well-knowntechnique involves monitoring zero voltage crossings in the back EMF ofthe unenergized motor winding, which can be used to establish theposition of the rotor, which is then fed back to the commutating circuitto provide proper commutation sequence to the stator windings.Difficulties are encountered, however, due to EMF interference in thewinding caused by the driven windings, and filters added to reduce theinterference themselves introduce delay and cost. Improvement insensorless control is therefore desirable, and it is an object of thepresent invention to provide such improvement.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a motor system comprising astator, the stator having at least a first and a second multiphasewinding, the first and second windings being electrically isolated fromone another and non-interlaced with one another, a rotor mounted formovement relative to the stator, the rotor having at least one permanentmagnet mounted thereon, a drive circuit including a power source and acommutation circuit, the drive circuit electrically connected to atleast the first winding to, in use, provide electricity to the firstwinding to rotationally drive the rotor about the axis, and a rotorposition recognition circuit connected to the second winding, the rotorposition recognition circuit adapted to, in use, determine rotorposition based on an electricity induced in the second winding when therotor passes the second winding, the rotor position recognition circuitconnected to drive circuit for providing feedback information to thedrive circuit regarding said determined rotor position.

In another aspect, the invention provides an electric motor systemcomprising a rotor mounted for rotation about an axis, the rotor havingat least one permanent magnet mounted thereon, a generally cylindricalstator, the stator having at least a first and second sector relative tothe rotor rotation axis, the first and second sectors being distinctfrom one another, the stator having at least two multiphase windingsets, wherein the at least two winding sets are confined to a differentone of said sectors, a motor drive connected to a power source and oneof the windings sets to thereby selectively energized the winding set toelectrically drive rotation of the rotor, and a rotor position decoderconnected to the other winding set to thereby acquire signals from theother winding for providing rotor position information to the motordrive.

In another aspect, the invention provides a motor system comprising apermanent magnet rotor, stator having at least a first multiphasewinding set and a second multiphase winding set, the first and secondwinding sets substantially electrically and magnetically isolated fromone another, the first set positioned in the stator such that, in use,magnetism induced by electricity flowing therethrough causes the rotorto rotate, the second positioned in the stator such that, in use, therotating rotor induces electricity to flow therethrough, a first controlsystem adapted to provide electricity to the first winding set tocontinuously drive rotation of the rotor, and a second control systemadapted to receive electricity induced in the second windings andprovide rotor position information to the first control system.

In another aspect, the invention provides a motor system comprising apermanent magnet rotor, a stator having at least a first multiphasewinding set and a second multiphase winding set, the first and secondwinding sets substantially electrically and magnetically isolated fromone another, a motor drive connected to a power source and the firstwinding sets to thereby selectively energized the first winding set toelectrically drive rotation of the rotor, and a rotor position decoderconnected between the second winding set and the motor drive to therebyacquire signals from the second winding for providing rotor positioninformation to the motor drive.

In another aspect, the invention provides a brushless motor systemcomprising at least a first magnetic circuit including at least a firstpermanent magnet rotor mounted for rotation on a shaft, a first statoradjacent the first rotor, and at least one multiphase winding setassociated with the first stator, at least a second magnetic circuitincluding at least a second permanent magnet rotor mounted for rotationon the shaft, a second stator adjacent the second rotor, and at leastone multiphase winding set associated with the second stator, the secondstator winding set being electrically isolated from the first statorwinding set, the second magnetic circuit being isolated from the firstmagnetic circuit, a commutation apparatus adapted to, in use, providecommutation signals to the first winding to cause the first winding setto drive rotation of the first rotor; and a rotor position sensingapparatus adapted to, in use, receive input from the second winding setand provide output rotor position information to the commutationapparatus.

In another aspect, the invention provides a method of operating a motorsystem, the system having at least a motor, a commutation apparatus, arotor position detecting apparatus and a source of electricity, themotor having at least a rotor and a stator, the method comprising thesteps of providing at least two multiphase winding sets in the stator,electrically isolating the at least two multiphase winding sets from oneanother, providing electricity from the commutation apparatus to atleast a first winding set of said at least two winding sets to therebycontinuously drive rotor rotation with said at least first winding set,leaving at least a second winding set of said at least two winding setscontinuously unenergized such that said rotor rotation induceselectricity in the second winding set, providing said inducedelectricity to the rotor position detecting apparatus to produce rotorposition information, and providing said rotor position information tothe commutation apparatus for at least one of verifying and adjusting acommutation process conducted by the commutation apparatus.

In another aspect, the invention provides a method of controlling amotor comprising the steps of providing commutation signals to at leasta first multiphase winding set in a stator to rotate a permanent magnetrotor, receiving rotor-induced electricity in at least a secondmultiphase winding set, the second multiphase winding set magneticallyisolated from the first set, using said received electricity todetermine information on a position of the rotor, and using saidposition information as an input in controlling the motor.

In another aspect, the invention provides a method of operating a motor,the motor having a permanent magnet rotor and a stator, the statorhaving at least a first multiphase winding set and a second multiphasewinding set, the first and second winding sets substantiallyelectrically and magnetically isolated from one another, the methodcomprising the steps of providing commutation signals to the firstwinding set to rotate a permanent magnet rotor, providing no inputelectricity to the second winding set, receiving rotor-inducedelectricity from second multiphase winding set, determining rotorposition information from the rotor-induced electricity, using saidinformation to adjust the commutation signals.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show moreclearly how it may be carried into effect, reference will now be made byway of example to the accompanying drawings showing articles madeaccording to preferred embodiments of the present invention, in which:

FIG. 1 is a schematic representation of a motor and control systemaccording to the present invention;

FIG. 2 a is a schematic representation of a portion of the motor andcontrol system of FIG. 1;

FIG. 2 b is a schematic representation of a portion of the controlsystem of FIG. 1;

FIG. 3 a is a cross-section and FIG. 3 b is an exploded isometric viewof a motor of the system of FIG. 1;

FIG. 3 c is a schematic representation of the a control system of theembodiment of FIGS. 3 a-3 b;

FIG. 4 is an exploded isometric view of an alternate construction forthe motor of FIG. 1;

FIGS. 5 a and 5 b are front and rear isometric views of the stator of,and FIG. 5 c is an exploded isometric view of, a further alternateconstruction for the motor of FIG. 1;

FIGS. 6 a and 6 b are each cross-sections of further alternateconstructions for the motor of FIG. 1;

FIG. 7 is a side view of a gas turbine engine incorporating the presentinvention, with a portion of the engine broken away to reveal across-section thereof; and

FIG. 8 is a schematic representation of a further embodiment of thepresent system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is suited for use with the machine configurationsdescribed in the applicant's co-pending applications Ser. No.10/444,952, filed 27 May 2003, and 10/452,135 filed 3 June 2003, thecontents of both of which are incorporated into this description byreference.

Referring to FIG. 1, a permanent magnet synchronous motor (PMSM) system10 includes a brushless permanent magnet machine 12, which has a “split”construction in that it includes magnetically and electrically isolatedstator winding sets 14 a and 14 b within associated stator portions 16 aand 16 b, respectively. Winding set 14 a and 14 b are independentlycontrollable such that machine 12 is essentially two distinct machines12 preferably within one casing (not shown), and having only a rotatablemagnetic rotor 18 as a common component. Rotor 18 is independentlyexcited, preferably having permanent magnets mounted thereto (not shown)in an manner well understood in the art. Winding sets 14 a and 14 b arepreferably each three-phase winding sets and are sequentiallydistributed circumferentially around stator, so that sets 14 a and 14 bare non-interlaced and do not overlap, and thus are spatially remote anddistinctly positioned from each other. Machine 12 is connected to a load20 (see FIG. 2), a power source 22, a motor drive commutation circuit 24and a rotor position recognition circuit 26.

Referring to FIG. 2 a, three-phase winding set 14 a is electricallyconnected to power source 22 via commutation circuit 24, and three-phasewinding set 14 b is preferably also selectively connected to powersource 22 via commutation circuit 24 (the selective connection beingconnoted by the stippled line). Winding set 14 b is also electricallyconnected to rotor position recognition circuit 26 which is, in turn,connected for feedback communication with commutation circuit 24.

In use, the motor is started, as described in more detail below. Oncethe motor is running, power provided by source 22 is commutated bycommutation circuit 24 and supplied to one set of windings, say windingset 14 a, to thereby drive rotor 18 and cause the machine 12 to operateas a motor. As rotor 18 passes the undriven set of windings, in thisexample 14 b, the motion of the magnet in rotor 18 relative to windings14 b induces EMF in windings 14 b (windings 14 b, being undriven,therefore act as a sort of generator), which induced EMF is usedaccording to the present invention by rotor position recognition circuit26 to determine rotor position, as will be described further below.Rotor position may then be determined, and this feedback is thenprovided to the commutating circuit 24 so that the excitation currentprovided to winding set 14 a may be properly timed and adjusted, if andas necessary, to drive windings 14 a to produce the desired outputtorque, etc. from machine 12.

EMF signals induced in windings 14 b are fed to an appropriate circuit26 for determination of rotor position based on the induced EMF signals.Any suitable method of determining rotor position from the inducedsignals may be used. In an analog embodiment, a voltage comparator (notshown) is used to compare the signal against a reference input of 0 V todetermine the zero-crossings, representative of the 0° and 180°positions in a sine wave induced voltage. In a digital embodiment (notshown), the induced analog voltage is converted to a digital signal andfed to an appropriate circuit for detection of the appropriate value. Ineither case, a circuit which is suitable for use in determining rotorposition based on signals received from three Hall sensors may be usedand fed appropriately with preferably conditioned signals (see below)from windings 14 b to determine rotor position, once rotor rotation hasstarted. In a preferred embodiment, the functional operations of motordrive and commutation circuit 24 and a rotor position sensing circuit 26are accomplished through the use of commercially available brushlessmotor controllers, such as Motorola Inc.'s MC33035 Brushless MotorController shown in FIG. 2 b. The skilled reader will appreciate, inlight of this disclosure herein, that some signal conditioning (notshown) may be desired or required for the input signals for such acontroller (e.g. variable voltage input sine wave converted to a fixedamplitude square wave of the type typically produced by a Hall sensor).

Initially motor 12 must be started in order to get rotor 18 movingrelative to stator 16, so that EMF is induced in windings 14 b and sothat rotor 18 position can be determined. Initially the position ofrotor 18 is unknown. For starting motor 12, therefore, the system is runin a starting or ‘jogging’ mode, which is performed open loop (i.e. withno position feedback), and relies on the polar moment of inertia inconjunction with the torque-current constant of the motor to startrotation of rotor 18. In essence, a rotor position is assumed and thecommutation signal is provided appropriately preferably to both windings14 a and 14 b, in order to provide enough torque to begin movement ofthe rotor. Once rotor 18 is thus ‘jogged’ (i.e. moved), this movementresults in a signal induced in windings 14 a and 14 b that is thendetectable as a position signal (particularly in the unenergizedwindings), as described above, and the operation of commutation circuit24 can be adjusted accordingly to bring the motor up to speed. Theapproach may be an iterative one (i.e. the rotor may not start rotatingas desired on the first ‘jog’), and thus several successive attempts mayneed to be made in order to start the desired rotation of rotor 18. Onewinding set 14, or all winding sets 14, can be driven as describedinitially. Furthermore, unenergized windings in either set 14 can beused as the “sensor” in the start mode. Preferably, however, only oneset (e.g. 14 a) is driven on a given start, and then the other set (e.g.14 b) is driven on the next start and so on. In the event that there isa failed function(s) in either the motoring or sensing functions of thewinding sets, this can be detected and can be addressed. In the case ofthe gas turbine shown in FIG. 7 and described below, preferably thisfault detection can be accomplished before engine-start is accomplished.

If both winding sets 14 a and 14 b are used to start motor, oncerotation begins to occur, preferably as one phase of winding set 14 b(in this example) is de-energized, the induced EMF is fed to rotorposition recognition circuit 26 to permit the position of rotor 18 to bedetermined. Finally, once motor 12 approaches a condition wheresufficient torque may be provided entirely by winding set 14 a (in thisexample), winding set 14 b is completely de-energized and thereafterundriven to then provide the three-phase rotor position recognitionfunction, as described initially above.

The present invention, therefore, teaches in one aspect the provisionand use of at least one winding, and preferably a three-phase windingset, which is electrically and magnetically isolated from the activewindings in the motor for use in decoding and recognizing rotor positionin PMSM motor. The invention thus permits more accurate and simplerrotor position recognition because the signal provided for analysis isreduced in noise, without reliance on filters, and thus permits zeroesto be more accurately counted, leading to improved motor control.

Additional embodiments are possible. Throughout this description asvarious embodiments are described, each embodiment is provided withreference numerals in successive “100s” series (e.g. 100, 200, 300,etc.). Features in later embodiments similar to those in earlierembodiments are given the same basic reference number in successiveseries as in the original series (e.g. rotor 18 and rotors 118, 218,318, etc.). Where the construction and/or operation of such embodimentfeatures is not described further below, the reader may assume thatconstruction and operation are as described above, having regard tothose modifications apparent to those skilled in the art. Also, for easeof reference, each winding set and its associated electromagnetic systemare occasionally referred to as “channels”, such that machine 12 may bedescribed as a “dual channel” motor, having two electromagneticallyisolated “channels” or winding sets.

Referring to FIGS. 3 a and 3 b, PMSM machine 112 is shown, havingindependent three-phase winding sets 114 a and 114 b, a cylindricalstator 116 and a cylindrical rotor 118 mounted for rotational motionrelative to the stator. Winding sets 114 a and 114 b, together withtheir corresponding stator portions, provide two separateelectromagnetic systems 130 a and 130 b, by reason of the windings'electrical isolation from one another. Rotor 118 has permanent magnets140 mounted by a retaining ring 142 to a rotatable shaft 144. Stator 116has a plurality of teeth 146 separating adjacent windings. (For ease ofillustration, the adjacent elements of windings 114 a and 114 b in FIG.3 b are shown unconnected.). As depicted in FIG. 3 c, in a similarmanner as described above winding set 114 a is electrically connected topower source 122 via commutation circuit 124, and winding set 114 b ispreferably also selectively connected to power source 122 viacommutation circuit 124. Referring to FIG. 3 c, preferably a motor driveand commutation circuit 24 and a rotor position sensing circuit 26 isprovided for each winding set, such that circuits 24 a and 24 b and 26 aand 26 b are provided. The rotor position circuits 26 arecross-connected (e.g. 26 b to 24 a and 26 a to 24 b) so that either (orboth) set of windings may be driven and that the signals sensed from theinactive set are fed to properly commute the driven set. PMSM 112 mayotherwise be conventional in its construction, as desired. PMSM may alsobe made in accordance with the teachings of the applicant's U.S. Pat.No. 6,313,560, also incorporated into this disclosure by reference.

Referring to FIG. 4, in another embodiment motor 212 is shown in an“outside rotor” dual channel configuration, in which rotor 218 surroundsstator 216. Stator 216 has winding sets 214 a and 214 b. Stator 216 hasa rotor-facing surface 216′. Though not depicted in FIG. 4, winding set214 a is electrically connected to power source 314 (not shown) viacommutation circuit 224 (not shown), and winding set 214 b is preferablyalso selectively connected to power source 222 via commutation circuit224. Winding set 214 b is also similarly electrically connected to rotorposition recognition circuit 226 (not shown) which is, in turn,connected for feedback communication with commutation circuit 224.

Referring to FIGS. 5 a-5 c, an outside-rotor, 3-phase, dual channel PMSMmotor is provided with a “primary” and “secondary” winding configurationand machine architecture as described in detail in the applicant'sco-pending application Ser. No. 10/444,952, incorporated herein byreference. The details of the construction and operation of thisembodiment are fully described in the incorporated reference, and thusneed only be summarily described here. For clarity, it should be notedthat FIGS. 5 a-5 c omit one winding set or channel to more easily depictthe construction of the device.

PMSM 312 has primary winding sets 314 a and 314 b (314 b not shown forclarity), in stator 316 surrounded by a rotor 318 (see 5 c). Twoseparate channels 330 a and 330 b are provided by reason of theelectrical isolation of winding sets 314 a and 314 b. As also apparentfrom the figures, the two channels are also spatially remote from oneanother, providing magnetic isolation.

Referring to FIG. 5 a, in this embodiment three primary windings 314 aare provided, namely primary windings 314 a ¹, 314 a ² and 314 a ³, toprovide the desired 3-phase configuration. Each primary winding 314 a isprovided with its own primary terminal 356 a for ease of connection topower source 322 and commutation circuit 324 (neither shown). Likewise,primary windings 314 b (not shown) have terminals for connection tocommutation circuit 324 and rotor position recognition circuit 326 (notshown) in a similar manner as described above. Primary windings 314 aand 314 b are provided between stator teeth 360 in slots 362, and arewrapped around a bridge portion 364 provided in slot 360. Preferablypaper spacers 366 are provided for insulation. In addition to primarywinding sets 314 a and 314 b, stator 316 also has secondary windingssets 350 a and 350 b each have squirrel cage-type arrangement (i.e. withlegs 352 and end rings 354).

Bridges 364 are preferably non-integral with stator 316, and thusinserted as an assembly as depicted schematically in FIG. 5 c, whichadvantageously permits the designer to select different materials forbridge 364 and stator 316. For example, a bridge material may be chosento alter the magnetic or performance characteristics of motor 312, as isdiscussed in application Ser. No. 10/444,952. Non-integral bridges 364may also beneficially facilitate motor assembly, as explained furtherbelow.

Referring to FIGS. 6 a and 6 b, various arrangements and numbers ofchannels can be provided in the motor. In FIG. 6 a, channel 430 adominates the machine layout, while channel 430 b is restricted to onesector of the stator. As above, the two channels are substantiallymagnetically isolated and spatially remote from one another. Referringto FIG. 6 b, multiple channels 430 a-430 f are provided, each having adiffering number of phases. In either case, the channels may beconnected to commutation circuits and/or rotor position recognitioncircuits (neither shown), as desired in light of the teachings above.

Referring to FIG. 7, the present invention is particularly well suited,among other things, to act as a starter 512 driving a shaft 502 to startgas turbine engine 500, as depicted in an integral embodiment in FIG. 7.A non-integral starter (not shown) is also available, as will beunderstood by the skilled reader.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, though preferred the invention does not require a 3-phaseinput signals, and may be used with any multiphase winding. Athree-phase winding set is preferred because it simplifies theassociated electronics by allowing the use of commercially-availableintegrated circuits designed to be used with 3 Hall sensors to senserotor position.

In the above description, in steady-state motor operation one channel isused to drive the motor, while the other channel is used for recognizingrotor position. It will be understood that both channels could be usedfor motoring, for example if added torque is required, preferably aslong as unenergized phase(s) are monitored as described above for rotorposition. More than two channels may be provided to the motor, and thechannels need not be symmetric or of equal size. More than one rotorposition recognition circuit and/or channel may be provided, and somechannels may be used for other purposes not described herein. The statorneed not be slotted. Though described with reference to a synchronousalternating current permanent magnet motor, the present invention may beapplied to all types brushless permanent magnet motors. The common rotormay in fact be multiple rotors on a common shaft, such that the positionsensing of one rotor will permit the position of all rotors on the shaftto be determined.

In another dual channel embodiment (FIG. 8), the second channel orwinding set may share the same slot as the first channel or main windingbut be electrically isolated from the main winding set. The flux in theundriven windings induced by the rotor magnets would typically besignificantly greater than the flux induced by adjacent windingcurrents, and current/voltage transformation and signal processing canbe used to improve the input rotor position signal.

Still other modifications which fall within the scope of the presentinvention will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the equivalents accorded to the appended claims.

1. A motor system comprising: a stator, the stator having at least afirst and a second multiphase winding, the first and second windingsbeing electrically isolated from one another and non-interlaced with oneanother; a rotor mounted for movement relative to the stator, the rotorhaving at least one permanent magnet mounted thereon; a drive circuitincluding a power source and a commutation circuit, the drive circuitelectrically connected to at least the first winding to, in use, provideelectricity to the first winding to rotationally drive the rotor aboutthe axis; and a rotor position recognition circuit connected to thesecond winding, the rotor position recognition circuit adapted to, inuse, determine rotor position based on an electricity induced in thesecond winding when the rotor passes the second winding, the rotorposition recognition circuit connected to drive circuit for providingfeedback information to the drive circuit regarding said determinedrotor position.
 2. The motor system of claim 1 wherein the first andsecond windings have at least three phases.
 3. The motor system of claim1 wherein the first and second windings are spaced apart from oneanother.
 4. The motor system of claim 1 wherein the first and secondwindings occupy non-overlapping sector segments of the stator.
 5. Anelectric motor system comprising: a rotor mounted for rotation about anaxis, the rotor having at least one permanent magnet mounted thereon; agenerally cylindrical stator, the stator having at least a first andsecond sector relative to the rotor rotation axis, the first and secondsectors being distinct from one another, the stator having at least twomultiphase winding sets, wherein the at least two winding sets areconfined to a different one of said sectors; a motor drive connected toa power source and one of the windings sets to thereby selectivelyenergized the winding set to electrically drive rotation of the rotor;and a rotor position decoder connected to the other winding set tothereby acquire signals from the other winding set for providing rotorposition information to the motor drive.
 6. The motor system of claim 5wherein said other winding set is not connected to the motor drive.
 7. Amotor system comprising: a permanent magnet rotor; stator having atleast a first multiphase winding set and a second multiphase windingset, the first and second winding sets substantially electrically andmagnetically isolated from one another, the first set positioned in thestator such that, in use, magnetism induced by electricity flowingtherethrough causes the rotor to rotate, the second positioned in thestator such that, in use, the rotating rotor induces electricity to flowtherethrough; a first control system adapted to provide electricity tothe first winding set to continuously drive rotation of the rotor; and asecond control system adapted to receive electricity induced in thesecond windings and provide rotor position information to the firstcontrol system.
 8. The motor system of claim 7 further comprising: athird control system adapted to provide electricity to the secondwinding set to continuously drive rotation of the rotor; a fourthcontrol system adapted to receive electricity induced in the firstwindings and provide rotor position information to the third controlsystem.
 9. A motor system comprising: a permanent magnet rotor; statorhaving at least a first multiphase winding set and a second multiphasewinding set, the first and second winding sets substantiallyelectrically and magnetically isolated from one another; a motor driveconnected to a power source and the first winding set to therebyselectively energized the first winding set to electrically driverotation of the rotor; and a rotor position decoder connected betweenthe second winding set and the motor drive to thereby acquire signalsfrom the second winding set for providing rotor position information tothe motor drive.
 10. The motor system of claim 9 wherein the first andsecond windings are disposed in distinct sectors of the stator.
 11. Themotor system of claim 9 wherein at least a portion of the first andsecond windings are non-overlapping relative to each other in thestator.
 12. The motor system of claim 9 wherein the first and secondwindings sets are arranged serially with one another relative to apermanent magnet rotation path of the rotor.
 13. The motor system ofclaim 9 wherein each winding set is a 3-phase winding set.
 14. The motorsystem of claim 9 further comprising a commutation apparatus connectedto the first winding set and a rotor position sensing apparatusconnected to the second winding set, wherein the rotor position sensingapparatus is connected to commutation apparatus for providing rotorposition feedback information to the commutation apparatus.
 15. Abrushless motor system comprising: at least a first magnetic circuitincluding at least a first permanent magnet rotor mounted for rotationon a shaft, a first stator adjacent the first rotor, and at least onemultiphase winding set associated with the first stator; at least asecond magnetic circuit including at least a second permanent magnetrotor mounted for rotation on the shaft, a second stator adjacent thesecond rotor, and at least one multiphase winding set associated withthe second stator, the second stator winding set being electricallyisolated from the first stator winding set, the second magnetic circuitbeing isolated from the first magnetic circuit; a commutation apparatusadapted to, in use, provide commutation signals to the first statorwinding set to cause the first stator winding set to drive rotation ofthe first rotor; and a rotor position sensing apparatus adapted to, inuse, receive input from the second stator winding set and provide outputrotor position information to the commutation apparatus.
 16. The motorsystem of claim 15 wherein the first and second rotors are the samerotor.
 17. The motor system of claim 16 wherein the first and secondstators are portions of the same stator body.
 18. The motor system ofclaim 16 wherein the first and second stators are distinct sectors ofthe same stator body.
 19. The motor system of claim 18 wherein only saidtwo magnetic circuits and said two multiphase winding sets are provided,and wherein the first and second stators each occupy a different half ofthe stator body.
 20. A method of operating a motor system, the systemhaving at least a motor, a commutation apparatus, a rotor positiondetecting apparatus and a source of electricity, the motor having atleast a rotor and a stator, the method comprising the steps of:providing at least two multiphase winding sets in the stator;electrically isolating the at least two multiphase winding sets from oneanother; providing electricity from the commutation apparatus to atleast a first winding set of said at least two winding sets to therebycontinuously drive rotor rotation with said at least first winding set;leaving at least a second winding set of said at least two winding setscontinuously unenergized such that said rotor rotation induceselectricity in the second winding set; providing said inducedelectricity to the rotor position detecting apparatus to produce rotorposition information; and providing said rotor position information tothe commutation apparatus for at least one of verifying and adjusting acommutation process conducted by the commutation apparatus.
 21. Themethod of claim 20 further comprising the step of magnetically isolatingthe at least two multiphase winding sets from one another.
 22. A methodof controlling a motor comprising the steps of: providing commutationsignals to at least a first multiphase winding set in a stator to rotatea permanent magnet rotor; receiving rotor-induced electricity in atleast a second multiphase winding set, the second multiphase winding setmagnetically isolated from the first set; using said receivedelectricity to determine information on a position of the rotor; andusing said position information as an input in controlling the motor.23. A method of operating a motor, the motor having a permanent magnetrotor and a stator, the stator having at least a first multiphasewinding set and a second multiphase winding set, the first and secondwinding sets substantially electrically and magnetically isolated fromone another, the method comprising the steps of: providing commutationsignals to the first winding set to rotate a permanent magnet rotor;providing no input electricity to the second winding set; receivingrotor-induced electricity from second multiphase winding set;determining rotor position information from the rotor-inducedelectricity; and using said information to adjust the commutationsignals.